Four new dimeric aporphinoids named bidebilines A-D (1-4), bis-7,7'-dehydroanonaine (1), 7-dehydroanonaine-7'-dehydro-8'-methoxyanonaine (2), bis-7,7'-dehydro-8,8'-dimethoxyanonaine (3), and bis-7,7'-dehydro-10,10'-dimethoxyanonaine (4), were isolated from the roots of Polyalthia debilis. Their structures were established on the basis of spectral evidence. Compounds 3 and 4 exhibited moderate antimalarial activity with IC50 values of 5.4 and 4.1 mg/mL, respectively.